Apparatus for measuring body fluid pressure

ABSTRACT

The apparatus for measuring body fluid pressure consists of a three-way stopcock in which any two of the three arms may be connected together at any one time. One arm of the stopcock is connected to body pressure through a tube and a second arm is connected to a chamber containing a small pressure-sensitive transducer. A third arm is connected containing a sealable passage through which sterile saline solution is introduced to the tube and chamber and which also connects atmospheric pressure to the chamber for calibration purposes. The third passage can be closed by a self-resealable plug which permits the injection of an anticoagulant into the apparatus.

United States Patent [72] Inventor Eugene Temkin Long Beach, Calit. [21]Appl. No. 607,767 [22] Filed Jan. 6, 1967 [45] Patented Oct. 5, 1971[73] Assignee The Birtcher Corporation Los Angeles, Calif.

[54] APPARATUS FOR MEASURING BODY FLUID PRESSURE 1 Claim, 6 DrawingFigs.

[52] U.S. Cl 128/2.05 D, 73/398 [51] Int. Cl A6111 5/02 [50] Field ofSearch. 128/205, 194, 215, 218.1 P, 214, 2.05 D, 2.05 E; 73/388, 398

[56] References Cited UNITED STATES PATENTS 2,535,998 12/1950 Bierman128/2.05 X 2,600,324 6/1952 Rappaport 128/205 X Primary Examiner-RichardA. Gaudet Assistant Examiner-Kyle L. Howell Attorney-Robert E. GeauqueABSTRACT: The apparatus for measuring body fluid pressure consists of athree-way stopcock in which any two of the three arms may be connectedtogether at any one time. One arm of the stopcock is connected to bodypressure through a tube and a second arm is connected to a chambercontaining a small pressure-sensitive transducer. A third arm isconnected containing a sealable passage through which sterile salinesolution is introduced to the tube and chamber and which also connectsatmospheric pressure to the chamber for calibration purposes. The thirdpassage can be closed by a self-resealable plug which permits theinjection of an anticoagulant into the apparatus.

APPARATUS FOR MEASURING BODY FLUID PRESSURE This invention relates tomedical apparatus, and, more particularly, to apparatus for measuringcontinuously or intermittently, as desired, internal body fluidpressure, such as blood pressure or spinal fluid pressure.

Although there has long been a need for indirect means of continuouslyor intermittently measuring blood pressure automatically, such as byautomatic inflation of blood pressure cuffs and audio pickups to recordthe pressure, practical means have not been developed thus far. Suchmeans as have been developed have not been practical from the standpointof reliability, instrumentation, and accuracy.

Several direct methods of continuously or intermittently measuring bloodpressure, involving direct contact of the apparatus with the patientsblood, have been developed, but these have had several drawbacks. In onetechnique, one end of a long polyethylene or Teflon tube filled with anaqueous solution is inserted into the patients artery or other bloodvessel. The other end of the tube is connected to a pressure-sensitivetransducer. The plastic tube is quite inelastic and the column of fluidtransmits the pressure pulses through the tube to the transducer. Thistechnique has several disadvantages. First, the adjustment of thetransducer is a very complicated procedure. Its accuracy and sensitivitydepend upon careful adjustment and balance. Second, the length of theplastic tube which transmits the pressure through the column of waterdetermines the accuracy of the instrument. Third, the equipment requiredis bulky and requires specially trained laboratory personnel to use iteffectively. Fourth, in open heart surgery many feet of tubing are addedto the already complex equipment required. Fifth, patient movement andmanipulation of the tubing constitutes a patient hazard, since he maypull the tubing out of the blood vessel, and the accuracy of thereadings may be adversely affected.

Another known technique involves the use of a pressure transducermounted in that end of a tube that is inserted into a patients bloodvessel. Although this technique does avoid several of the disadvantagesof the first technique mentioned, it is still not possible to calibratethe apparatus to atmospheric pressure without removing the pressuretransducer from the patients blood vessel.

The present invention obviates the foregoing disadvantages of prior artdevices. This is accomplished by utilizing valve means such as athree-way stopcock, which is adapted to be fixed on the patients bodynear the point at which the pres sure is being measured. The stopcockmay be mounted on a small plate and secured to a patients arm or leg bymeans of adhesive tape. It can also be plugged into a spinal needle inthe case of measuring spinal fluid pressure.

The stopcock has three arms, each having a passage therethrough, withany two of the arms being connectable together at any time by means of arotatable valve having an external handle for rotating the valve. Onethe arms is conneeted to a short length of plastic tubing which isinserted into the patients body (into, for example, an artery) where itis desired to measure pressure transmitted through a fluid. A second oneof the arms may be utilized for introducing an anticoagulant into theapparatus and for calibrating the system to atmospheric pressure. Thethird arm is directly connected to a contained pressure transducer.

The transducer, which is an exceedingly small interface, is mounted inthe third arm of the stopcock and is thus very close to the point atwhich pressure is to be measured. Only a single small diameter cable isused to electrically connect the transducer to a suitable amplifierwhich is connected into a recording apparatus such as a recordinggalvanometer or a standard electrocardiograph. Various utilization meansmay be used, such as high and low limit alerting devices, and theinvention is in no way limited to the use of any particular device orequipment.

By requiring only the use of a single small lead from the patients bodyto the utilization equipment, the apparatus of the invention becomesparticularly adaptable to use during operations where the operating roomis crowded with equipment, and any additional complexities should beheld to a minimum. The apparatusdoes not require the use of laboratorypersonnel to operate it. It can be calibrated and operated by a nursewith a minimum of special training.

The invention, together with further features and advantages, will bebetter understood from the following description, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of the apparatus of the invention mountedon a patients forearm;

FIG. 2 is a perspective view of a stopcock embodying the invention;

FIG. 3 is a horizontal sectional view taken on the line 3-3 of FIG. 2;

FIG. 4 is a partially sectional plan view of the apparatus of theinvention showing the stopcock valve in a position to permit injectionof a fluid into the apparatus;

FIG. 5 is a plan view showing the apparatus mounted on a patients backfor measuring spinal fluid pressure; and

FIG. 6 is a sample graph from utilization equipment showing calibrationmarks.

As shown in FIG. 1, the apparatus embodying the invention comprisesvalve means such as a three-way stopcock, indicated generally by thenumeral l0,'which is mounted on a small plate 12. The plate 12 issecured to a forearm 14 of a patient by means of adhesive tape 16. Onearm of the stopcock 10 is connected to one and of a catheter or plastictube I8, whose other end is inserted into a vein, artery, a spinal canalin the patient. A thin cable 20 leads from another arm of the stopcock10 to the input of a suitable amplifier 22, whose output is connected toa readout device 24, such as an electrocardiograph or an oscilloscope.

The amplifier 22 may contain a conventional electrical bridge, which isbalanced when the signal thereto from the stopcock 10 is zero. Astandard resistor 26 of a desired value may be connected across one legof the bridge through a switch 28 to serve as a calibration means. Forexample, the value of the resistor 26 may be so choosen that, when nosignal is received from the stopcock l0 and the switch 28 is closed, thereadout device may indicate a reading corresponding to to mm. of mercuryor any other suitable pressure range that is desired. Thus, when theconnection between the stopcock l0 and the patients fluid is closed off,a direct connection to the atmosphere is made so as to permit acalibration to zero. The amplifier is entirely conventional, and servesmerely to amplify any output signal from the bridge.

The readout device 44 may be a conventional recording galvanometer, andelectrocardiograph, or other device that preferably provides a permanentrecord of the pressure being measured. The bridge and amplifier and thereadout device comprise utilization means.

FIGS. 2 and 3 illustrate the three-way stopcock 10 in detail. As shown,the stopcock includes a central body member 30, three arms 32, 34, and36 disposed 90 apart, and a central rotatable valve member 38 providedwith a handle 40 for turning the valve member. The stopcock I0 issecured to the plate 12 by screws (not shown) extending through spacers42, or by other suitable means. The method of mounting the stopcock onthe plate is of no particular importance, however. The arms 32, 34, and36 are provided with central passages 32a, 34a, and 360, respectively,which communicate within the valve member 38. The valve member 38 isprovided with a T-shaped passage 38a, so that any two of the passages32a, 34a, 36a may be connected together at any one time. Stops areprovided so that all three passages 32a, 34a, 36a, cannot be connectedtogether.

The plastic tube 18 and its appropriate connecting adapter fit over theend of the arm 32 with an airtight seal. The passage 34a in the arm 34is closed by closure means such as a stopper or a plug 44 with a rubbercap or the like through which a hypodermic needle may be inserted (seeFIG. 4) but which is self-resealable and closes off the passageway 34afrom the atmosphere.

Three-way stopcocks of the type utilized in the present invention arewell known and are available as standard equipment from any medicalsupply house. Various models may differ from each other in minordetails, and it is to be understood that the stopcock 10 shown herein isfor purposes of illustration only, and the invention is in no waylimited to the use of that particular design or construction.

Referring again to FIGS. 2 and 3, it is seen that the external end ofthe arm 36 of the stopcock is externally threaded, as at 36b, and anadapter 46 is threaded onto the arm 36. The opening 36a in the am isenlarged as shown at 36c and is constructed to receive the smallpressure-sensitive transducer 48, which is of conventional, well-knowndesign. The pressure forces exerted by the column of fluid on thetransducers surface develop a voltage which is proportional to the forceexerted upon it. This charge is transmitted to the amplifier 22 and thusprovides a signal to the readout device 24.

To assemble the apparatus for use, all the air is removed from thestopcock, so that it does not cushion any force exerted against thetransducer 48, by connecting a syringe filled with sterile saline to thearm 34. The passageways are then filled with the saline by rotating thevalve 38. After the passageways 34a, 38a, 36a, and 36c are filled withsaline, the transducer 48 is dipped into the fluid and secured in place.The tube 18 is connected to the patient in the desired manner andquickly fills with blood or other body fluid. it is then connected tothe arm 32 of the stopcock l0, and with the stopcock 38 in a positionconnecting passageways 34a and 32a, the saline is injected through thearm 34 and 32 and into the tubing 18 so as to clear the blood from itand return it to the patient's body. This last procedure is notnecessary in the case of measurements involving noncoagulating bodyfluids. A suitable plug 44 or cap may now be placed on arm 34. Ananticoagulant such as Heparin may then be introduced with a syringe andneedle through the plug or cap 44 and will fill the tube 18 so as toprovide a noncoagulating interface between the blood and the fluid inthe tubing. The valve may then be -tumed to connect the passages 32a and36a and the apparatus is ready for use except for calibration.

The pressure measuring apparatus of the invention may be calibratedintennittently as desired by rotating the valve 38 to connect thepassages 34a and 36a, and then removing the plug or cap 44 from the arm34. This subjects the transducer 48 to atmospheric pressure through thesaline column in the anns 34 and 36, and serves to establish the zerobase line. The readout device 24 can then be adjusted to read zero underthis condition with the valve still connecting the passages 34a and 36a.The switch 28 can then be closed and deflection calibration of thereadout device adjusted to its correct sensitivity for the range ofpressures desired. The valve 38 is then rotated to connect the passages32a and 36a, the passage 34a is refilled with saline if necessary, andthe plug or cap 44 is replaced in the arm 34. The apparatus is now readyfor use.

FIG. 6 illustrates a typical graph that might be obtained from thereadout device 24. As shown in the FlG., portion 58 of the curverepresents the base line calibration, when the transducer is connectedto the atmosphere through the saline column and arm 34 of the stopcock.Portion 60 of the curve represents the output when the switch 28 isclosed to represent a given pressure in terms of mm. of mercury or wateras the case may be. The portion 62 represents the recorded reading ofthe patient's fluid pressure with the passages 32a and 36a connectedtogether.

FIG. 5 shows the apparatus of the invention applied to the measurementof a patients spinal fluid pressure. The apparatus is attached to thestandard customarily used spinal needle 18' (in the fashion of the tube18 in FIGS. 1-3). The spinal needle is previously inserted into thespinal canal by the operator, and the spinal fluid will now emit fromthe needles external end. No modification of the apparatus is necessaryto measure and record spinal fluid pressures, although the apparatus maybe recalibrated for the suitable pressure range of spinal fluiddynamics. During the measurement, spinal fluid samples as customarilytaken ma be removed through the arm 34 by turning the valve 38. ftersampling IS done, the

valve 38 is again turned so as to connect passageways 32a and 36a and tomeasure the final pressures after withdrawal of specified amounts ofspinal fluid.

It is now apparent that the apparatus of the invention fills a long-feltneed in the art. it avoids the use of long lengths of tubing by beinglocated very close to the point of the patient's body where pressure isbeing measured. The apparatus is compact and light in weight and iseasily operated, and is connected to the utilization means only by asmall cable. Anticoagulants can be readily introduced into the apparatusto prevent clotting and consequent false readings and/or inoperability.It can monitor fluid pressure continuously or intermittently, as isdesired, and can be calibrated without removing the connection from apatient's body for extended periods of time.

Although one embodiment has been illustrated and described in detail, itis apparent that many changes and modifications can be made thereinwithout departing from the true scope and spirit of the invention.

What is claimed is:

1. Apparatus for measuring the pressure of a body fluid comprising:

a body member including first, second and third conduit arms;

a threeway valve positioned in said body member and being positionableto interconnect any two of said first, second and third conduit arms;

means connected to said first arm and being in communication with saidbody fluid for directing the pressure of the body fluid to said valve;

a chamber disposed in communication with aid second conduit arm;

sealable passage means connected to said third arm for introducingsaline solution into said connecting means when said valve connects saidfirst and third arms and into said chamber when said valve connects saidsecond and third arms and for connecting atmospheric pressure to saidchamber when said valve connects said second and third arms;

a pressure-sensitive transducer located in said chamber for providingoutput signals indicative of the pressure of the body fluid when saidvalve connects said first and second arms;

circuit means connected to said pressure-sensitive transducer forproducing an indication of the magnitude of the output signal receivedfrom said pressure-sensitive transducer; and

a self-resealable plug for selectively sealing said passage means andpermitting injection of an anticoagulant therethrough.

1. Apparatus for measuring the pressure of a body fluid comprising: a body member including first, second and third conduit arms; a three-way valve positioned in said body member and being positionable to interconnect any two of said first, second and third conduit arms; means connected to said first arm and being in communication with said body fluid for directing tHe pressure of the body fluid to said valve; a chamber disposed in communication with aid second conduit arm; sealable passage means connected to said third arm for introducing saline solution into said connecting means when said valve connects said first and third arms and into said chamber when said valve connects said second and third arms and for connecting atmospheric pressure to said chamber when said valve connects said second and third arms; a pressure-sensitive transducer located in said chamber for providing output signals indicative of the pressure of the body fluid when said valve connects said first and second arms; circuit means connected to said pressure-sensitive transducer for producing an indication of the magnitude of the output signal received from said pressure-sensitive transducer; and a self-resealable plug for selectively sealing said passage means and permitting injection of an anticoagulant therethrough. 